I have 3 tables,which are not created with the ON DELETE CASCADE option, nor is it an option to create them as such.
I may need to delete from all three tables in succession. Is there a way to do this using only the promotion_id as a key? Because I need to delete in reverse order, the promotion_id is gone by the time I get to the dependent tables.
I am thinking that the only way to do this is to SELECT the keys of the 3 tables using a JOIN, and then use them individually. But it would be nice if there was a pure SQL solution to it.
I am using JDBC, Spring, and Oracle. Thanks.
create table test_rates (
rate_id varchar2(10) primary key,
rate number
);
create table test_offers (
offer_id varchar2(10) primary key ,
rate_id varchar2(10),
foreign key (rate_id) references test_rates (rate_id)
);
create table test_promotions (
promotion_id varchar2(10) primary key ,
offer_id varchar2(10),
foreign key (offer_id) references test_offers (offer_id)
);
insert into test_rates (rate_id,rate) values (1,199);
insert into test_offers (offer_id,rate_id) values (11,1);
insert into test_promotions (promotion_id,offer_id) values (21,11);
commit;
delete from test_promotions where promotion_id = 21;
delete from test_offers where offer_id in (select offer_id from test_promotions where promotion_id = 1); -- key is gone by now
In the common case, when there are N promotions (N>1) for a single offer, it wouldn't make sense to delete the offer if one promotion only is deleted. You would end up with orphaned promotions.
If you want to delete a rate, it would make sense to start with deleting all children promotions then all children offers then delete the rate. In that case though, the rate_id could be used along the way.
If you delete a child record, there's no need to delete the parent record unless of course this is a requirement, in which case start with looking for the parent id and see above.
Related
I'm working on a project in which I'm writing queries from this database that I am attempting to create in PLSQL. However, before I can do that I must create the db, and some of the table-create statemens I'm trying to run are returning errors. Specifically, the errors seem to indicate that some of the primary keys I'm referencing don't exist. When I check to see if that is true I see the likely issue. For example, I try to do
create table group_disforum ( df_id int,
ig_id int,
constraint gdf_FK foreign key(ig_id) references Course_Interest_group(interest_gid),
constraint gdf_PK primary key(df_id, ig_id),
comments varchar(150)
)
setting the foreign key to the primary key(interest_gid) in Course_Interest_group.
However, the Course_Interest_group is this:
create table Course_Interest_group( interest_gid int,
gname varchar(20),
courseid int,
facultyid int,
past_gpa float,
constraint IG_PK primary key(interest_gid, courseid, facultyid),
constraint IG_FK1 foreign key(courseid) references course(courseid),
constraint IG_FK2 foreign key(facultyid) references User_Faculty(userid)
);
The primary key for Course_Interest_group is not just interest_gid, but interest_gid, courseid, and facultyid.
There are several other instances of the same issue.
My question is, when referencing Course_Interest_group how can I reference just interest_gid? Is it possible? Should I change something?
I would like to keep the current Course_Interest_group pk of (interest_gid, courseid, facultyid) intact but I will modify it if needed.
my code
my output
If in the course_interest_group table interest_gid uniquely identifies each row in the table then interest_gid should be the primary key. Similarly, in the group_disforum if df_id uniquely identifies each row in the table then df_id should be the primary key. Modifying the primary keys of both these tables should solve the issue.
I think the way around for your question will be a TRIGGER to customize the data Integrity. You can create a before INSERT Trigger which will check first whether the data in your case (Course_Interest_group(interest_gid)). So basic structure of your Trigger will be like. Hope this may be a workwround.
SET SQLBL ON;
SET DEFINE OFF;
CREATE OR REPLACE TRIGGER group_disforum_tg BEFORE
INSERT OR
UPDATE
/*OF ig_id*/
ON group_disforum FOR EACH ROW
DECLARE lv_chck PLS_INTEGER;
BEGIN
SELECT COUNT(1)
INTO lv_chck
FROM Course_Interest_group
WHERE interest_gid = :new.interest_gid;
IF lv_chck = 0 THEN
RAISE_APPLICATION_ERROR(-20001,'Parent key (interest_gid) not found in group_disforum_tg',TRUE);
END IF;
END;
/
I'm wondering is it possible to use a constraint to set the value of one column to be sum of two others. For example given the following tables:
CREATE TABLE Room (
Room_Num NUMBER(3),
Room_Band_ID NUMBER(2),
Room_Type_ID NUMBER(2),
Room_Price NUMBER(4),
PRIMARY KEY (Room_Num),
FOREIGN KEY(Room_Band_ID)
REFERENCES Room_Band(Room_Band_ID),
FOREIGN KEY(Room_Type_ID)
REFERENCES Room_Type(Room_Type_ID)
);
CREATE TABLE Booking (
Booking_ID NUMBER(10) NOT NULL,
GuestID NUMBER(4) NOT NULL,
StaffID NUMBER(2) NOT NULL,
Payment_ID NUMBER(4) NOT NULL,
Room_Num NUMBER(3) NOT NULL,
CheckInDate DATE NOT NULL,
CheckOutDate DATE NOT NULL,
Booking NUMBER(2) NOT NULL,
Price NUMBER(4),
PRIMARY KEY (Booking_ID),
FOREIGN KEY(GuestID)
REFERENCES Guest(GuestID),
FOREIGN KEY(StaffID)
REFERENCES Staff(StaffID),
FOREIGN KEY(Payment_ID)
REFERENCES Payment(Payment_ID),
FOREIGN KEY(Room_Num)
REFERENCES Room(Room_Num)
);
I know it is possible to do something like:
Constraint PriceIs CHECK (Booking.Price=(Room.Room_Price*
(Booking.CheckOutDate - Booking.CheckInDate)));
Is it also possible to set up a constraint that doesn't just ensure that the price is correct, but to calculate the price automatically into the price field for the relevant tuple?
Update,
So I've tried to set up a trigger as follows:
CREATE OR REPLACE trigger PriceCompute
AFTER INSERT ON Booking
FOR each row
BEGIN
UPDATE Booking
SET
SELECT (Room.Room_Price*(Booking.CheckOutDate - Booking.CheckInDate))
INTO
Booking.Price
FROM Booking
JOIN ROOM ON Booking.Room_Num = Room.Room_Num
END;
/
But I'm getting the following errors back:
Can anyone see where I'm going astray here, as its beyond me.
Yes, you can. Here are your options. Listed in order of my personal preference:
You can have a table without this column. And create a view that will be calculating this column on a fly.
You may use oracle virtual columns
create table Room (
...
price NUMBER GENERATED ALWAYS AS (room_price*(checkOut-checkIn)) VIRTUAL,
...)
You may use actual column (same as 2, per Dave Costa):
create table Room (
...
price AS (room_price*(checkOut-checkIn)),
...)
You can write trigger to populate it (like Mat M suggested)
You can write stored procedure, but it will be an overkill in this situation
I think you would have to put a trigger on both tables for whenever the price value of the room is changed or the checkout/in dates are changed, it will update the PriceIs field from your calculation.
If you don't need the calculated portion stored in an actual field, you can always create a view that calculates it whenever you look at the view.
I think the better solution is to use a view that calculates the value on the fly. But regarding your attempt to create a trigger, you should use :new.<column_name> to refer to the values being inserted into the Booking table. You don't need to perform updates and queries on that table to get or modify the values in the row that is being inserted*. You just refer to them as variables. So you would want to do something like:
SELECT (Room.Room_Price*(:new.CheckOutDate - :new.CheckInDate))
INTO
:new.Price
FROM ROOM WHERE :new.Room_Num = Room.Room_Num
*In fact, you can't perform queries or updates on the table whose modification invoked the trigger in the first place. You would get the infamous "mutating table" error if your trigger actually compiled and ran.
I want update book ant set amount-1, when after insert record to sell table.
create table book (
id number(3) not null,
name varchar(20),
author varchar(12),
amount number(3) not null,
constraint book_pk primary key(id)
);
create table sell (
id number(3) not null,
date varchar(20),
book_id number(3),
constraint sell_pk primary key(id)
);
I want after insert to table sell record update book table amount-1;
CREATE OR REPLACE TRIGER changes_amount_trigger
AFTER INSERT ON sell
FOR EACH ROW
BEGIN
UPDATE BOOK SET amount = amount-1 WHERE id = book_id
END;
I not know how to get inserted record book id, to update this record in book table.
Try like this,
CREATE OR REPLACE TRIGGER changes_amount_trigger
AFTER INSERT ON sell
FOR EACH ROW
BEGIN
UPDATE BOOK SET amount = amount-1 WHERE id = :new.book_id;
END;
/
Data Model Assumptions:
I am assuming you will register transactions by changing the data in the SELL table through INSERT DML SQL operations. This is also supported by your set up of a DML trigger on SELL to pass its changes as SALES information to the BOOK table. This is workable.
By accident, I tried setting up the trigger a little differently and I'd like to suggest a different approach:
Consider possibly working in the opposite direction: Change book quantities directly on the BOOK table, so a single purchase of book_id = 5 would handle queries that could:
UPDATE book SET amount = amount -1
WHERE id = 5; COMMIT;
Restocking would mean increasing the quantity of available books
by incrementing the AMOUNT value instead.
There are a few additional changes that might tighten up this two-table design and protect the integrity of the data within them for the longer term:
CREATE TABLE book (
id number(3) not null,
name varchar(20),
author varchar(12),
amount number(3) not null,
CONSTRAINT book_pk PRIMARY KEY(id)
);
ALTER TABLE book
ADD CONSTRAINT book_amt_ck CHECK (amount > 0);
ALTER TABLE book
ENABLE CONSTRAINT book_amt_ck;
To prevent negative book amount (quantity) values, a TABLE CHECK CONSTRAINT would prevent the entry of values by means of arithmetic errors in DML operations such as:
UPDATE book SET amount := amount - 1
In the example above, there is no control over decrementing the book inventory even if the quantity on hand has reached 0. Check out a few references on TABLE CHECK CONSTRAINTS to get a better understanding of what it can do for specific design situations.
Here are some design suggestions for the trigger:
Changes in book quantities should be the only triggering data element that affects the SELL table.
The trigger should account for changes in book quantities > 1.
CREATE OR REPLACE TRIGGER orders_after_update
AFTER UPDATE
ON book
FOR EACH ROW
DECLARE
v_amount number;
BEGIN
IF (:new.amount < :old.amount ) THEN
FOR v_amount in 1 .. (:old.amount - :new.amount)
LOOP
INSERT INTO sell (id, date, book_id)
VALUES (sell_seq.nextval, sysdate, :new.id);
COMMIT;
END LOOP;
END IF;
END;
For more information on triggers and their design, check a few instances to get a better understanding of how they are designed and set up.
CREATE SEQUENCE sell_seq
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 20;
We needed a sequence to populate the primary key/index of the SELL table. Oracle Sequences are useful for this purpose.
By watching the table changes with a trigger on the BOOK table, you can use the built in references which already exist when a table trigger fires. For example, BOOK.ID does not require an additional query because a trigger automatically is made aware of the beginning and ending value of each trigger monitored record.
Some useful discussions on triggers are discussed in more detail through an Internet search.
Setting Up a Foreign Key Relationship
Although the trigger will probably keep this relation clean, a Foreign Key relation between elements BOOK.ID and SELL.BOOK_ID would be good, otherwise queries on Sales transactions may yield book sales without any descriptive production information. The following is a reference on Foreign Keys and their use.
CREATE TABLE sell (
id number(3) not null,
date varchar(20),
book_id number(3)
);
ALTER TABLE table_name
ADD CONSTRAINT sell_fk
FOREIGN KEY (book_id)
REFERENCES book(id);
Do you already have records in sell table and want to update the amount in book table ?
if this is your case you can update your book.amount as following:
update book b
set b.amount = b.amount - (select count(*) from sell s where b.id = s.book_id);
I want to create a trigger, in Oracle. When the dateOrdReceived in my order table is updated or inserted the trigger takes this date whatever it may be and updates it by 14 days into another table productList ordDateDelivery so that it equals to
dateOrdReceived + 14 days = new ordDateDelivery
I did have a couple of attempts and guessed I'd need a query which would join my two tables. I also learned that maybe using DATEADD would allow me add 14 days but altogether I can't quite get it right.
My trigger attempt
`CREATE OR REPLACE TRIGGER "PRODUCTLIST_DATE_DELIVERY"
BEFORE
insert or update on "PRODUCTLIST"
for each row
begin
select p.dateOrdRecieved, o.ordDateDelivery
from productList p JOIN orders o
ON p.ordID = o.ordID;
new.OrdDateDelivery := DATEADD(day,14,new.p.dateOrdRecieved)
end;
/
ALTER TRIGGER "PRODUCTLIST_DELIVERY_DATE" ENABLE
and my tables for this trigger are as follows
PRODUCTLIST TABLE
CREATE TABLE "PRODUCTLIST"
( "ORDID" NUMBER(3,0) NOT NULL ENABLE,
"PRODUCTID" NUMBER(3,0) NOT NULL ENABLE,
"QUANTITY" NUMBER(4,2) NOT NULL ENABLE,
"ORDDATEDELIVERY" DATE,
"DISCOUNT" NUMBER(3,0),
"TOTALCOST" NUMBER(4,2),
CONSTRAINT "PK_PRODUCTLIST" PRIMARY KEY ("ORDID", "PRODUCTID") ENABLE
)
/
ALTER TABLE "PRODUCTLIST" ADD CONSTRAINT "FK_ORDERS" FOREIGN KEY ("ORDID")
REFERENCES "ORDERS" ("ORDID") ENABLE
/
ALTER TABLE "PRODUCTLIST" ADD CONSTRAINT "FK_PRODUCTS" FOREIGN KEY ("PRODUCTID")
REFERENCES "PRODUCT" ("PRODUCTID") ENABLE
/
ORDERS TABLE
CREATE TABLE "ORDERS"
( "ORDID" NUMBER(3,0) NOT NULL ENABLE,
"DATEORDRECIEVED" DATE,
"CUSID" NUMBER(3,0) NOT NULL ENABLE,
PRIMARY KEY ("ORDID") ENABLE
)
/
ALTER TABLE "ORDERS" ADD CONSTRAINT "FK_CUSTOMER" FOREIGN KEY ("CUSID")
REFERENCES "CUSTOMER" ("CUSID") ENABLE
/
DATEADD() is not an Oracle function... Oracle's datetime arithmetic is based around the day. If you add 1 to a date it increments the date by one day, adding 1.5 by 36 hours etc.
Now, your trigger.
You can't automatically update or insert a record into another table. The trigger is "on" one table, which means you need to create the DML in order to add or update it into that table.
update productlist
set dateOrdRecieved = :new.OrdDateDelivery + 14
where ordid = :new.ordid
The :new. here references the new data of the table on which the trigger is on. It's a specific "variable" that you can access rather than a general concept of what you're trying to achieve. You can't use it to assign data to other tables directly, though you can use it as a means of doing so.
Next you need to consider where your trigger is. You're looking to update PRODUCTLIST whenever ORDERS is changed, this means that the trigger needs to be on the table ORDERS.
create or replace trigger productlist_date_delivery
before insert or update on orders
for each row
begin
update productlist
set OrdDateDelivery = :new.dateOrdRecieved + 14
where ordid = :new.ordid;
end;
/
Notice a few extra differences to your own:
I use :new. instead of new.
I'm not selecting from the table; there's no need to do this as the data is already available. It's also impossible as you're selecting data that Oracle's trying to update, it forbids this to ensure integrity.
I haven't used cased identifiers. There's no need to do this; Oracle upper-cases everything by default. It's also really painful if everything's not upper case as you have to remember
Every statement ends in a semi-colon.
If you're having problems I recommend Tech on the Net, it has a good basic guide. As always though, there's the documentation on the CREATE TRIGGER statement.
I'm working on a set of database tables in Oracle and trying to figure out a way to enforce referential integrity with slightly polymorphic data.
Specifically, I have a bunch of different tables--hypothetically, let's say I have Apples, Bananas, Oranges, Tangerines, Grapes, and a hundred more types of fruit. Now I'm trying to make a table which describes performing steps involving a fruit. So I want to insert one row that says "eat Apple ID 100", then another row which says "peel Banana ID 250", then another row which says "refrigerate Tangerine ID 500", and so on.
Historically, we've done this in two ways:
1 - Include a column for each possible type of fruit. Use a check constraint to ensure that all but one column is NULL. Use foreign keys to ensure referential integrity to our fruit. So in my hypothetical example, we'd have a table with columns ACTION, APPLEID, BANANAID, ORANGEID, TANGERINEID, and GRAPEID. For the first action, we'd have a row 'Eat', 100, NULL, NULL, NULL, NULL, NULL. For the second action, we'd have 'Peel', NULL, 250, NULL, NULL, NULL. etc. etc.
This approach is great for getting all of Oracle's RI benefits automatically, but it just doesn't scale to a hundred types of fruit. You end up getting too many columns to be practical. Just figuring out which type of fruit you are dealing with becomes a challenge.
2 - Include a column with the name of the fruit, and a column with a fruit ID. This works also, but there isn't any way (AFAIK) to have Oracle enforce the validity of the data in any way. So our columns would be ACTION, FRUITTYPE, and FRUITID. The row data would be 'Eat', 'Apple', 100, then 'Peel', 'Banana', 250, etc. But there's nothing preventing someone from deleting Apple ID 100, or inserting a step saying 'Eat', 'Apple', 90000000 even though we don't have an Apple with that ID.
Is there a way to avoid maintaining a separate column per each individual fruit type, but still preserve most the benefits of foreign keys? (Or technically, I could be convinced to use a hundred columns if I can hide the complexity with a neat trick somehow. It just has to look sane in day-to-day use.)
CLARIFICATION: In our actual logic, the "fruits" are totally disparate tables with very little commonality. Think customers, employees, meetings, rooms, buildings, asset tags, etc. The list of steps is supposed to be free-form and allow users to specify actions on any of these things. If we had one table which contained each of these unrelated things, I wouldn't have a problem, but it would also be a really weird design.
It's not clear to me why you need to identify the FRUIT_TYPE on the TASKS table. On the face of it that's just a poor (de-normalised) data model.
In my experience, the best way of modelling this sort of data is with a super-type for the generic thing (FRUIT in your example) and sub-types for the specifics (APPLE, GRAPE, BANANA). This allows us to store common attributes in one place while recording the particular attributes for each instance.
Here is the super-type table:
create table fruits
(fruit_id number not null
, fruit_type varchar2(10) not null
, constraint fruit_pk primary key (fruit_id)
, constraint fruit_uk unique (fruit_id, fruit_type)
, constraint fruit_ck check (fruit_type in ('GRAPE', 'APPLE', 'BANANA'))
)
/
FRUITS has a primary key and a compound unique key. We need the primary key for use in foreign key constraints, because compound keys are a pain in the neck. Except when they are not, which is the situation with these sub-type tables. Here we use the unique key as the reference, because by constraining the value of FRUIT_TYPE in the sub-type we can guarantee that records in the GRAPES table map to FRUITS records of type 'GRAPE', etc.
create table grapes
(fruit_id number not null
, fruit_type varchar2(10) not null default 'GRAPE'
, seedless_yn not null char(1) default 'Y'
, colour varchar2(5) not null
, constraint grape_pk primary key (fruit_id)
, constraint grape_ck check (fruit_type = 'GRAPE')
, constraint grape_fruit_fk foreign key (fruit_id, fruit_type)
references fruit (fruit_id, fruit_type)
, constraint grape_flg_ck check (seedless_yn in ('Y', 'N'))
)
/
create table apples
(fruit_id number not null
, fruit_type varchar2(10) not null
, apple_type varchar2(10) not null default 'APPLE'
, constraint apple_pk primary key (fruit_id)
, constraint apple_ck check (fruit_type = 'APPLE')
, constraint apple_fruit_fk foreign key (fruit_id, fruit_type)
references fruit (fruit_id, fruit_type)
, constraint apple_type_ck check (apple_type in ('EATING', 'COOKING', 'CIDER'))
)
/
create table bananas
(fruit_id number not null
, fruit_type varchar2(10) not null default 'BANANA'
, constraint banana_pk primary key (fruit_id)
, constraint banana_ck check (fruit_type = 'BANANA')
, constraint banana_fruit_fk foreign key (fruit_id, fruit_type)
references fruit (fruit_id, fruit_type)
)
/
In 11g we can make FRUIT_TYPE a virtual column for the sub-type and do away with the check constraint.
So, now we need a table for task types ('Peel', 'Refrigerate', 'Eat ', etc).
create table task_types
(task_code varchar2(4) not null
, task_descr varchar2(40) not null
, constraint task_type_pk primary key (task_code)
)
/
And the actual TASKS table is a simple intersection between FRUITS and TASK_TYPES.
create table tasks
(task_code varchar2(4) not null
, fruit_id number not null
, constraint task_pk primary key (task_code, fruit_id)
, constraint task_task_fk ask foreign key (task_code)
references task_types (task_code)
, constraint task_fruit_fk foreign key (fruit_id)
references fruit (fruit_id)
/
If this does not satisfy your needs please edit your question to include more information.
"... if you want different tasks for different fruits..."
Yes I wondered whether that was the motivation underlying the OP's posted design. But usually workflow is a lot more difficult than that: some tasks will apply to all fruits, some will only apply to (say) fruits which come in bunches, others will only be relevant to bananas.
"In our actual logic, the 'fruits' are totally disparate tables with
very little commonality. Think customers, employees, meetings, rooms,
buildings, asset tags, etc. The list of steps is supposed to be
free-form and allow users to specify actions on any of these things."
So you have a bunch of existing tables. You want to be able to assign records from these tables to tasks in a freewheeling style yet be able to guarantee the identify of the specific record which owns the task.
I think you still need a generic table to hold an ID for the actor in the task, but you will need to link it to the other tables somehow. Here is how I might approach it:
Soem sample existing tables:
create table customers
(cust_id number not null
, cname varchar2(100) not null
, constraint cust_pk primary key (fruit_id)
)
/
create table employees
(emp_no number not null
, ename varchar2(30) not null
, constraint emp_pk primary key (fruit_id)
)
/
A generic table to hold actors:
create table actors
(actor_id number not null
, constraint actor_pk primary key (actor_id)
)
/
Now, you need intersection tables to associate your existing tables with the new one:
create table cust_actors
(cust_id number not null
, actor_id number not null
, constraint cust_actor_pk primary key (cust_id, actor_id)
, constraint cust_actor_cust_fk foreign key (cust_id)
references customers (cust_id)
, constraint cust_actor_actor_fk foreign key (actor_id)
references actors (actor_id)
)
/
create table emp_actors
(emp_no number not null
, actor_id number not null
, constraint emp_actor_pk primary key (emp_no, actor_id)
, constraint emp_actor_emp_fk foreign key (emp_no)
references eployees (emp_no)
, constraint cust_actor_actor_fk foreign key (actor_id)
references actors (actor_id)
)
/
The TASKS table is rather unsurprising, given what's gone before:
create table tasks
(task_code varchar2(4) not null
, actor_id number not null
, constraint task_pk primary key (task_code, actor_id)
, constraint task_task_fk ask foreign key (task_code)
references task_types (task_code)
, constraint task_actor_fk foreign key (actor_id)
references actors (actor_id)
/
I agree all those intersection tables look like a lot of overhead but there isn't any other way to enforce foreign key constraints. The additional snag is creating ACTORS and CUSTOMER_ACTORS records every time you create a record in CUSTOMERS. Ditto for deletions. The only good news is that you can generate all the code you need.
Is this solution better than a table with one hundred optional foreign keys? Perhaps not: it's a matter of taste. But I like it better than having no foreign keys at all. If there is on euniversal truth in database practice it is this: databases which rely on application code to enforce relational integrity are databases riddled with children referencing the wrong parent or referencing no parent at all.